Beam expansion with three-dimensional diffractive elements

ABSTRACT

The specification and drawings present a new apparatus and method for using a three-dimensional (3D) diffractive element (e.g., a 3D diffractive grating) for expanding in one or two dimensions the exit pupil of an optical beam in electronic devices. Various embodiments of the present invention can be applied, but are not limited, to forming images in virtual reality displays, to illuminating of displays (e.g., backlight illumination in liquid crystal displays) or keyboards, etc.

TECHNICAL FIELD

The present invention relates generally to electronic devices and, morespecifically, to a diffractive optics method that uses athree-dimensional (3D) diffractive element (e.g., a 3D diffractiongrating) for expanding the exit pupil of an optical beam.

BACKGROUND ART

In a typical virtual display arrangement (e.g., see PCT patentapplication WO 99/52002 “Holographic Optical Devices” by Yaakov Amitaiand Asher Friesem and U.S. Pat. No. 6,580,529 “Holographic OpticalDevices” by Yaakov Amitai and Asher Friesem), the virtual image istypically formed by using several separate linear diffraction gratings.Using separate diffraction elements makes manufacturing of such gratingassembly difficult and requires a precise definition of the gratingperiod (e.g., typically two different grating periods are used) and anangle between the periodic lines. Furthermore, it requires a lot ofspace and the diffraction efficiency is usually dependent onpolarization (e.g., strong or weak polarization).

DISCLOSURE OF THE INVENTION

According to a first aspect of the invention, an apparatus, comprises:

a substrate made of an optical material having a first surface and asecond surface; and

a three-dimensional diffractive element comprising a plurality of pixelsdisposed on the substrate, the three-dimensional diffractive elementcomprises:

-   -   at least one area configured to receive an input optical beam,        and    -   at least one further area configured to provide at least one        output optical beam with an exit pupil expanded in one or two        dimensions,

wherein at least part of the input optical beam is diffracted in the atleast one area to provide at least one optical beam substantially withinthe first and second surfaces, and

at least part of the at least one optical beam is further coupled out ofthe first or the second surface of the substrate by diffraction in theat least one further area to provide the at least one output opticalbeam.

According further to the first aspect of the invention, the at least onearea and at least one further area may be disposed on one surface, thefirst or the second surface, of the substrate.

According further to the first aspect of the invention, the at least onearea and at least one further area may be disposed on opposite surfacesof the substrate.

Still further according to the first aspect of the invention, each pixelof the plurality of the pixels may have a first width in one directionon the first or second surface, a second width in a perpendicular to theone direction on the first or second surface, and a height. Further, theheight of the pixels in the at least one area may be larger than in theat least one further area. Further still, a distance between the pixelsin the one direction and in the perpendicular to the one direction maybe equal for all the pixels and the first and second widths may be equalfor all the pixels.

According further to the first aspect of the invention, a distancebetween the pixels in the one direction and in the perpendicular to theone direction may not be equal in the at least one area. Further, thepixels in the at least one area may be configured to provide the atleast one optical beam substantially in the one direction if the inputoptical beam has a predetermined first wavelength, and to provide the atleast one optical beam substantially in the perpendicular to the onedirection if the input optical beam has a predetermined secondwavelength different from the predetermined first wavelength.

According still further to the first aspect of the invention, the atleast one area has pixels slanted at least in one direction, such thatthe at least one optical beam is substantially provided in the at leastone direction.

According still further to the first aspect of the invention, the atleast one area may have at least two types of pixels with an asymmetricshape and slanted in at least two different directions, such that oneportion of the at least one optical beam may be substantially providedin one of the at least two different directions and another portion ofthe at least one optical beam may be substantially provided in anotherof the at least two different directions. Further, the at least twodifferent directions may be 180 degrees apart.

According yet further still to the first aspect of the invention, theapparatus may further comprise: an absorbing material may be depositedon a surface of the substrate opposite to the surface of thethree-dimensional diffractive element and opposite to the at least onearea.

Yet still further according to the first aspect of the invention, theapparatus may further comprise: at least one intermediate area such thatthe at least part of the optical beam diffracted in the at least onearea may be first coupled to the at least one intermediate area, whichmay be configured to substantially couple, using a further diffractionin the at least one intermediate area, the at least part of thediffracted optical beam to the at least one further area to provide theoutput optical beam with a two-dimensional exit pupil expansion of theinput optical beam. Further, the three-dimensional diffractive elementmay comprise two of the at least two intermediate areas and two of thefurther diffractive elements to provide two substantially identicalimages with the expanded exit pupil in the two dimensions from an imagecomprised in the input optical beam, wherein a portion of the at leastpart of the input optical beam may be provided to each of the twointermediate areas which may be configured to substantially couple theportion to a corresponding further area of the two further areas forproviding the two substantially identical images. Further still, the atleast one intermediate area may have pixels slanted in at least onedirection, such that the at least one optical beam may be substantiallyprovided in the at least one direction towards the at least one furtherarea.

According to a second aspect of the invention, a method, comprises:receiving an input optical beam by at least one area of athree-dimensional diffractive element comprising a plurality of pixelsdisposed on a substrate made of an optical material; diffracting atleast part of the input optical beam in the at least one area to provideat least one optical beam substantially within the first and secondsurfaces; and coupling out at least part of the diffracted optical beamof the first or the second surface of the substrate by diffraction in atleast one further area of the three-dimensional diffractive element toprovide at least one output optical beam with an exit pupil expanded inone or two dimensions.

According further to the second aspect of the invention, the at leastone area and at least one further area may be disposed: a) on onesurface, the first or the second surface, of the substrate or b) onopposite surfaces of the substrate. Further, each pixel of the pluralityof the pixels may have a first width in one direction on the first orsecond surface, a second width in a perpendicular to the one directionon the first or second surface, and a height. Still further, the heightof the pixels in the at least one area may be larger than in the atleast one further area.

Further according to the second aspect of the invention, a distancebetween the pixels in the one direction and in the perpendicular to theone direction may not be equal.

Further, the pixels in the at least one area may be configured toprovide the at least one optical beam substantially in the one directionif the input optical beam has a predetermined first wavelength, and toprovide the at least one optical beam substantially in the perpendicularto the one direction if the input optical beam has a predeterminedsecond wavelength different from the predetermined first wavelength.

Still further according to the second aspect of the invention, the atleast one area may have pixels slanted at least in one direction, suchthat the at least one optical beam may be substantially provided in theat least one direction.

According further to the second aspect of the invention, before thecoupling out the at least part of the diffracted optical beam, themethod may comprise: further diffracting the at least part of theoptical beam diffracted in at least one intermediate area tosubstantially couple the at least part of the diffracted optical beam tothe at least one further area for providing the output optical beam witha two-dimensional exit pupil expansion of the input optical beam.Further, the three-dimensional diffractive element may comprise two ofthe at least two intermediate areas and two of the further diffractiveelements to provide two substantially identical images with the expandedexit pupil in the two dimensions from an image comprised in the inputoptical beam, wherein a portion of the at least part of the inputoptical beam may be provided to each of the two intermediate areas whichmay be configured to couple the portion to a corresponding further areaof the two further areas for providing the two substantially identicalimages. Further still, the at least one intermediate area may havepixels slanted in at least one direction, such that the at least oneoptical beam may be substantially provided in the at least one directiontowards the at least one further area.

According to a third aspect of the invention, an electronic device,comprises:

-   -   a data processing unit;    -   an optical engine operatively connected to the data processing        unit for receiving image data from the data processing unit;    -   a display device operatively connected to the optical engine for        forming an image based on the image data; and    -   a three-dimensional exit pupil expander comprising:

a substrate made of an optical material having a first surface and asecond surface; and

a three-dimensional diffractive element comprising a plurality of pixelsdisposed on the substrate, the three-dimensional diffractive elementcomprises:

-   -   at least one area configured to receive an input optical beam,        and    -   at least one further area configured to provide at least one        output optical beam with an exit pupil expanded in one or two        dimensions,

wherein at least part of the input optical beam is diffracted in the atleast one area to provide at least one optical beam substantially withinthe first and second surfaces, and

at least part of the at least one optical beam is further coupled out ofthe first or the second surface of the substrate by diffraction in theat least one further area to provide the at least one output opticalbeam.

Further according to the third aspect of the invention, each pixel ofthe plurality of the pixels may have a first width in one direction onthe first or second surface, a second width in a perpendicular to theone direction on the first or second surface, and a height.

Still further according to the third aspect of the invention, the heightof the pixels in the at least one area may be larger than in the atleast one further area.

According further to the third aspect of the invention, a distancebetween the pixels in the one direction and in the perpendicular to theone direction may not be equal in the at least one area.

According still further to the third aspect of the invention, the atleast one area may have pixels slanted at least in one direction, suchthat the at least one optical beam may be substantially provided in theat least one direction.

According to a fourth aspect of the invention, an electronic device,comprises:

-   -   a three-dimensional exit pupil expander comprising:        -   a substrate made of an optical material having a first            surface and a second surface; and        -   a three-dimensional diffractive element comprising a            plurality of pixels disposed on the substrate, the            three-dimensional diffractive element comprises:        -   at least one area configured to receive an input optical            beam, and        -   at least one further area configured to provide at least one            output optical beam with an exit pupil expanded in one or            two dimensions,        -   wherein at least part of the input optical beam is            diffracted in the at least one area to provide at least one            optical beam substantially within the first and second            surfaces, and        -   at least part of the at least one optical beam is further            coupled out of the first or the second surface of the            substrate by diffraction in the at least one further area to            provide the at least one output optical beam;    -   at least one component comprising the substrate; and    -   a light source driver, responsive to an illumination selection        signal, for providing a drive signal to a light source in the        component for providing the input optical beam.

According further to the fourth aspect of the invention, the at leastone component may be at least one of a liquid crystal display and akeyboard.

According to a fifth aspect of the invention, an apparatus, comprises:means for disposing, made of an optical material having a first surfaceand a second surface; and

three-dimensional means for diffraction, comprising a plurality ofpixels disposed on the means for disposing, the three-dimensional meansfor diffraction comprises:

-   -   at least one area configured to receive an input optical beam,        and    -   at least one further area configured to provide at least one        output optical beam with an exit pupil expanded in one or two        dimensions,

wherein at least part of the input optical beam is diffracted in the atleast one area to provide at least one optical beam substantially withinthe first and second surfaces, and

at least part of the at least one optical beam is further coupled out ofthe first or the second surface by diffraction in the at least onefurther area to provide the at least one output optical beam.

According further to the fifth aspect of the invention, the means fordisposing may be a substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the nature and objects of the presentinvention, reference is made to the following detailed description takenin conjunction with the following drawings, in which:

FIGS. 1 a through 1 c are schematic representations of an exit pupilbeam expander with 3D diffraction gratings, wherein FIGS. 1 b and 1 care magnified views (top and side views respectively) in a vicinity of acorner A of FIG. 1 a (top view), according to an embodiment of thepresent invention;

FIGS. 2 a through 2 c are schematic representations (cross sectionalviews) of an exit pupil beam expander with 3D diffraction gratingsshowing beam propagation from an in-coupling to an out-coupling area(FIGS. 2 a and 2 b) and beam propagation in the out-coupling area (FIG.2 c), according to an embodiment of the present invention;

FIG. 3 a is a schematic representation of a 3-dimensional exit pupilbeam expander for a two dimensional exit pupil expansion, according toan embodiment of the present invention;

FIG. 3 b is a schematic representation of an asymmetric in-couplinggrating area implemented as asymmetric slanted pixels, according to anembodiment of the present invention;

FIG. 4 is a schematic representation of a 3-dimensional exit pupil beamexpander using an alternative implementation, according to an embodimentof the present invention;

FIGS. 5 a and 5 b are schematic representations of a 3-dimensional exitpupil beam expander with different pixel periods in x and y directions,according to embodiments of the present invention; and

FIGS. 6 a and 6 b are schematic representations of an electronic devicehaving a 3-dimensional exit pupil expander for illumination (FIG. 6 a)and for a virtual reality display (FIG. 6 b), according to embodimentsof the present invention.

MODES FOR CARRYING OUT THE INVENTION

A new method and apparatus are presented for using a three-dimensional(3D) diffractive element (e.g., a 3D diffractive grating) for expandingin one or two dimensions the exit pupil of an optical beam in electronicdevices. Various embodiments of the present invention can be applied,but are not limited, to forming images in virtual reality displays, toilluminating of displays (e.g., backlight illumination in liquid crystaldisplays) or keyboards, etc. The embodiments of the present inventioncan be applied to a broad optical spectral range of optical beams butmost importantly to a visible part of the optical spectrum where theoptical beams are called light beams.

According to embodiments of the present invention, the optical device(e.g., the optical device can be a part of a virtual reality display ofan electronic device) can comprise a substrate made of an opticalmaterial having a first surface and a second surface and athree-dimensional diffractive element (3D) comprising a plurality of 3Dpixels disposed on the first or/and the second surface of the substrate.

Furthermore, according to an embodiment of the present invention, saidthree-dimensional diffractive element can comprise at least one areaconfigured to receive an input optical beam, and at least one furtherarea configured to provide at least one output optical beam out of thesubstrate with an exit pupil expanded in one or two dimensions comparedto the input optical beam. Thus, at least part of the input optical beamis diffracted in the at least one area to provide at least one opticalbeam substantially within the first and second surfaces substantiallydue to a total internal reflection, and at least part of the at leastone optical beam is further coupled out of the first or the secondsurface of the substrate by diffraction in the at least one further areafor providing the at least one output optical beam.

According to another embodiment, each pixel of the plurality of thepixels can have a first width in one direction (e.g., x direction) onthe first or second surface, a second width in a perpendicular to saidone direction (e.g., y direction) on the first or second surface, and aheight (e.g., in z direction perpendicular to the substrate surface).The first and second widths can be equal for all the pixels or unequalfor different pixels. Typically, the height of the pixels in the atleast one area can be larger than in the at least one further area(e.g., the height in the at least one area can be 300 nm and the heightin the at least one further area can be 50 nm).

According to further embodiments of the present invention, a distancebetween said pixels in the one direction (or it can be called x-period)and in the perpendicular to said one direction (or it can be calledy-period) can be equal for all said pixels or can be unequal. Forexample, x- and y-periods can be unequal in the at least one area, thusfacilitating wavelength dependent coupling in perpendicular directions xand y. For example, in case of unequal x- and y-periods, the pixels inthe at least one area can be configured to provide the at least oneoptical beam substantially in the one direction if the input opticalbeam has a predetermined first wavelength, and to provide the at leastone optical beam substantially in the perpendicular to said onedirection if the input optical beam has a predetermined secondwavelength different from said predetermined first wavelength (e.g., seeexample of FIG. 5 a).

According to embodiments of the present invention, the 3D pixels (ordiffractive pixels) can be manufactured using a variety of techniques,e.g., using electron beam lithography, holographic recording, dryetching, etc., and implemented using a variety of different types ofdiffraction pixel profiles (e.g., binary, triangular, sinusoidal, etc.).The diffractive pixels can be symmetric or asymmetric profiles in x andy directions relative to a perpendicular to the first and secondsurfaces of the substrate, e.g., when grooves of the pixels havedifferent slanted angles (i.e., pixels having non-vertical sidewall) inx and/or y directions for coupling an optical beam in a preferreddirection. Therefore, one possibility is to have slanted pixels in theat least one area (i.e., the in-coupling area), thus re-directing onlywanted components of the input optical beam in a predetermined direction(e.g., x or y direction) defined by a slanted pixel profile.

Furthermore, the at least one area can have at least two types of pixelswith an asymmetric shape and slanted in at least two differentdirections (e.g., 180 degrees apart), such that one portion of the atleast one optical beam is substantially provided in one of the at leasttwo different directions and another portion of said at least oneoptical beam is substantially provided in another of the at least twodifferent directions (see example shown in FIG. 3 b).

Moreover, according to another embodiment of the present invention, anabsorbing material can be deposited on a surface of the substrate,opposite to the surface with the disposed three-dimensional diffractiveelement and opposite to said at least one area, for absorbing opticalbeams propagating in unwanted directions for improving couplingefficiency in a desired direction (thus e.g., for improving opticalcontrast of images) as further demonstrated in FIG. 3 b.

According to the described embodiments, a uniform (i.e., havingidentical pixels and their periods throughout) three-dimensionaldiffraction grating can provide two-dimensional expansion of the exitpupil. However, many variations are possible. According to a furtherembodiment of the present invention, in order to provide more uniformtwo-dimensional expansion of the exit pupil of the input beam (e.g.,comprising a two-dimensional image) and/or for creating two or moreidentical images (e.g., for binocular and/or stereoscopic applications),at least one intermediate area can be used in the 3D diffractiveelement, such that the at least a part of the optical beam diffracted inthe at least one area is first coupled to the at least one intermediatearea, which then can substantially coupled, using a further diffractionin the at least one intermediate area, the at least part of saiddiffracted optical beam to the at least one further area for providingthe output optical beam for a two-dimensional exit pupil expansion ofthe input optical beam. Furthermore, the at least one intermediate areacan have pixels slanted in at least one direction, such that the atleast one optical beam is substantially provided in said at least onedirection towards the at least one further area.

Specifically, in case of the virtual reality display applications, thethree-dimensional diffractive element can comprise two (or more) of theat least two intermediate areas and two (or more) of the furtherdiffractive elements to provide two (or more) substantially identicalimages, with the exit pupil expanded in two dimensions, from an imagecomprised in the input optical beam, wherein a portion of the at leastpart of the input optical beam can be provided to each of the twointermediate areas which then can be substantially coupled to acorresponding further area of the two further areas for providing thetwo (or more) substantially identical images. Various examples areprovided in FIGS. 3 a, 3 b and 4.

The embodiments described herein allow using one 3D grating structure inorder to produce, e.g., a whole virtual display or backlightilluminating using a compact layout. Moreover, manufacturing of such 3Dstructure by using only one grating shape is simple and does not requirealignment of several gratings which are usually used in virtual realitydisplays. Furthermore, the diffraction efficiency of this 3D gratingstructure is estimated to be high.

Also, it is noted that various embodiments of the present inventionrecited herein can be used separately, combined or selectively combinedfor specific applications.

FIGS. 1 a and 1 b show examples among others of schematicrepresentations (top views) of a 3-dimensional exit pupil beam expander(EPE) 10, wherein FIGS. 1 b and 1 c are magnified views (top and sideviews respectively) in a vicinity of a corner A of FIG. 1 a, accordingto an embodiment of the present invention.

The 3D beam expander 10 is implemented as a 3D diffractive element(grating) 12 which comprises areas 12 a for entering by the inputoptical beam and 12 b for out-coupling the output optical beam, whereinthe 3D diffractive element is disposed on an optical substrate(waveguide) 11 (see FIG. 2 a or 2 b). In the example of FIGS. 1 a and 1b, only one pixel period is used, e.g., dx=dy=400 nm and the same 3Dgrating 12 can couple the light into the waveguide in the area 12 a andalso can couple the light out of the area 12 b.

FIG. 1 b shows the square grating pixel shape that is more or less anideal situation: in practice the pixel shape can have, e.g., elliptic orrounded boundaries. Moreover, the pixel grating structure can be, forexample, a binary grating (with vertical sidewalls) or a slanted grating(with non-vertical sidewalls). It is also noted that a shape of pixels14 is determined by widths cx and cy, a depth (see h1 and h2 in FIG. 2a), and a slanted angle (see FIG. 3 b), which can be adjusted as afunction of the location in the grating area to optimize the bestgrating performance. The grating fill-factor of the grating is definedby a ratio of cx or cy and corresponding pixel period dx or dy. Thedesign of the 3D pixel grating can be implemented by using rigorousdiffraction theory in order to evaluate the diffraction efficiencies ofthe gratings and/or ray tracing method in order to choose the best pixelgrating shape at each point in all areas of the 3D grating 12. FIGS. 1 band 1 c further demonstrate the beam propagation inside the substrate11. When an input optical beam 17 hits the grating surface, the beamwill be diffracted into 6 diffraction orders. In all cases the opticalbeams with diffraction orders R(−1,0) for reflected beam and T(−1,0) fortransmitted beam are diffracting out from the system as shown in FIG. 1c. Four more beams, e.g., R(0,0), R(−1,−1), R(−1, +1) and R(−2,0), asshown in FIGS. 1 b and 1 c, are propagating inside of the substrate(waveguide) 11. It is noted that the out-coupling occurs every time thebeam hits the grating surface and it cannot be totally avoided. However,the diffraction grating can be designed in such a manner that it willminimize the out-coupling and diffract more light, e.g., R(−1,+1) andR(−1,−1) diffraction orders, within the substrate 11. Thus, it isillustrated in FIGS. 1 b and 1 c how the same 3D diffraction grating canexpand the optical beam in two dimensions and simultaneously out-couplesthe output optical beam. It is noted that in the above example theincidence angle is substantially zero, if we have an oblique angle thecoupled beams are not propagating directly in x or y directions butstill 6 beams exist.

FIGS. 2 a through 2 c show further examples among others of schematicrepresentations (cross sectional views) of a 3-dimensional exit pupilbeam expander 10 showing beam propagation from the in-coupling area 12 ato the out-coupling area 12 b (FIGS. 2 a and 2 b) and beam propagationin the out-coupling area 12 b (FIG. 2 b), according to embodiments ofthe present invention.

For example, in the area 12 a the pixel height h1 can be relativelylarge (e.g., ˜300 nm) for providing a high coupling efficiency (acoupled optical beam is shown as a beam 17 a; the beam 17 a indicates apropagation direction of an optical power whereas the actual beam ispropagated by multiple reflection and/or diffraction in the waveguide11) of an input optical beam 17, and in the area 12 b the pixel heighth2 can be relatively small (e.g., ˜50 nm) for achieving a uniformout-coupling of the beams 18 and/or 18 a. FIG. 2 b demonstrates theembodiment when out-coupling area 12 b is disposed on another surface ofthe substrate 11 than the in-coupling area 12 a.

The light can be coupled out of the out-coupling area 12 b as shown inFIG. 2 c in detail. The amount of out-coupling at each time the beammeets the grating depends on the grating properties. The system can bedesigned so that at least for one wavelength and incoming angle theoutput is uniform, i.e. r₁=r₂= . . . , as shown in FIG. 2 c, wherein r₁,r₂, . . . and t₁, t₂, . . . are reflected and transmitted optical beamsout of the EPE 10, respectively, and I1, I2 . . . are reflected opticalbeams inside the EPE 10 by the total internal reflection.

FIG. 3 a shows an example among others of a schematic representation ofa 3-dimensional exit pupil beam expander 20 implemented as onediffractive element for a two-dimensional exit pupil expansion,according to an embodiment of the present invention. The input opticalbeam enters in the area 22 which couples two optical beams 34 a and 34 bin two opposite directions, e.g., along x axis, to intermediate areas 24a and 24 b, respectively. Then the beams 34 a and 34 b are coupled in aperpendicular direction, e.g., along y-axis (see optical beams 36 a and36 b), by the intermediate areas 24 a and 24 b (which can be optimizedfor high efficiency coupling, using, for instance, slanted pixels forthat direction based on a diffraction analysis and the designrequirements) to out-coupling areas 26 a and 26 b, respectively, toprovide two expanded substantially identical images of an imagecomprised in the input optical beam, thus providing the virtual realityimage. It is noted that the optical signal can “leak” out of theintermediate area (i.e., to be seen by a viewer) as explained in regardto FIGS. 1 b and 1 c.

Area 28 can be left without diffractive pixels or be coated with anabsorbing material to minimize contributions (i.e., coupled optical beamto the areas 26 a and 26 b) from the area 28 in the output optical beam.It is noted that area 28 can be also filled with the pixels. In thiscase, more power efficiency can be provided (i.e., more power is coupledto the areas 36 a and 36 b possibly at the expense of an image contrast.Also, if all pixels of the exit pupil beam expander 20 are identical, inprincipal the whole area of the expander 20 can be used for viewing animage expanded in two dimensions.

FIG. 3 b shows a schematic representation of an in-coupling grating area22, which can be used in the example of FIG. 3 a, implemented usingasymmetric slanted pixels divided into two parts 22 a and 22 b withasymmetric slanted angles adjacent to a line 30 as shown, according toan embodiment of the present invention. Then the input optical beam 17can be coupled as the beam 34 a substantially in one x direction by theslanted part 22 a and as the beam 34 b substantially in the opposite xdirection by the slanted part 22 a, for providing a high contrast of thetwo optical images comprised in the output optical beam.

The optical contrast can be further improved by providing an absorbingmaterial (e.g., an absorbing coating) 30 on a surface of the substrate11 opposite to the substrate surface with the area 22 in a vicinity ofthe line 30 (as shown in FIG. 3 b). If the width of the absorbing areais optimized to be small enough compared to the total width of the area22, only the unwanted optical beams will be absorbed. These unwantedbeams are the optical beams which are transmitted by the areas 22 a and22 b without diffracting and those diffracted beams that propagate inunwanted directions.

It is noted that the grating shape of the out-coupling and/orintermediate areas can be also slanted (slanted angle with respect to zaxis shown as line 30 in FIG. 3 b). The slanted angle can either be withrespect to x-direction, y-direction or an intermediate direction (whichdefines a slanted rotation angle as an angle between this intermediatedirection and the x-direction) depending on the appropriate design andapplication. For example, if a slanted pixel has the slanted angle of 4degrees and slanted rotation angle of 45 degrees, then the grating canreflect about 80% of light into one direction with the diffraction orderR(−1,−1). It is also noted that the grating shape (cx, cy, depth, andslanted angles) can be adjusted as a function of the location in thegrating area: The goal is to optimize the best grating performance forsufficient and equal intensity out-coupling and beam expansion.

FIG. 4 shows another example of a schematic representation of a3-dimensional exit pupil beam expander 20 a using anotherimplementation, according to an embodiment of the present invention.Here, each of the intermediate areas 24 a and 24 b (compare with FIG. 3a) couples, e.g., using slanted grating approach shown in FIG. 3 b,optical beams into two opposite directions: beams 36 a and 38 a arecoupled by the intermediate area 24 a to the corresponding out-couplingareas 26 a and 40 a and beams 36 b and 38 b are coupled by theintermediate area 24 b to the corresponding out-coupling areas 26 b and40 b. Thus the 3D EPE 20 a of FIG. 4 is configured to provide fourexpanded substantially identical images of an image comprised in theinput optical beam.

It is noted (similar to FIG. 3 a) that areas 28 and 28 a can be alsofilled with the pixels. In this case, more power efficiency can beprovided (i.e., more power is coupled to the out-coupling areas 36 a, 36b, 38 a and 38 b possibly at the expense of an image contrast.

FIG. 5 a is a schematic representation of a 3-dimensional exit pupilbeam expander 20 b with different pixel periods in x and y directions,according to embodiments of the present invention. The pixel period in xdirection (x-period) in the in-coupling area 52 is chosen to couple theoptical beams 58 a and 58 b substantially in the x direction to areas 54a and 54 b, respectively, if the input optical beam has a predeterminedfirst wavelength. The areas 54 a and 54 b can have pixel periods in xand/or y directions matching the x-direction pixel period of the area52. Similarly, the pixel period in y direction (which is different thanthe x-period) in the in-coupling area 52 is chosen to couple the opticalbeams 60 a and 60 b substantially in the y direction to areas 56 a and56 b, respectively, if the input optical beam has a predetermined secondwavelength, which is different than the first wavelength. The areas 56 aand 56 b can have pixel periods in x and/or y directions matching they-direction pixel period of the area 52. The areas 54 a, 54 b, 56 a and56 b can serve as out-coupling elements. Alternatively, these areas canserve as intermediated areas for creating two-dimensional exit pupilexpanders as shown in an example of FIG. 5 b. In FIG. 5 b, the beams 62a, 62 b, 64 a and 64 b are further coupled to corresponding out-couplingareas 66 a, 66 b, 68 a and 68 b. Thus, the out-coupling areas 66 a and66 b can provide two substantially identical images of the imagecomprised in the input optical beam at the first predeterminedwavelength, whereas the out-coupling areas 68 a and 68 b can provide twosubstantially identical images of the image comprised in the inputoptical beam at the second predetermined wavelength.

It is noted that in FIG. 5 a an area 66 indicated by a dotted line canbe completely covered with 3D identical grating pixels, so theperformance then will be similar to the example of FIG. 1 a.

It is noted that using different pixel periods in x and y directions inthe intermediate diffractive areas can also serve as a directionselective method for a one-wavelength operation.

FIG. 6 a shows an example among other possible applications of aschematic representation (or a block diagram) of an electronic device 70having a 3-dimensional exit pupil expander for a backlight illumination,e.g., in the liquid crystal display (LCD) 78 and/or in a keyboard 76,according to an embodiment of the present invention. In response to anappropriate instruction (e.g., from a user), a user interface andcontrol module 72 provides an illumination selection signal to a lightsource driver, which then provides an appropriate drive signal for abacklight illumination of the LCD 78 and/or the keyboard 76. The module72 can select, e.g., whether to illuminate the LCD 78, the keyboard 76or both and possibly with what color.

FIG. 6 b shows an example of a schematic representation of an electronicdevice, having the 3D exit pupil expander (EPE) 20, 20 a or 20 b,according to an embodiment of the present invention.

The 3D exit pupil expander (EPE) 20, 20 a or 20 b can be used in anelectronic (portable) device 100, such as a mobile phone, personaldigital assistant (PDA), communicator, portable Internet appliance,hand-hand computer, digital video and still camera, wearable computer,computer game device, specialized bring-to-the-eye product for viewingand other portable electronic devices. As shown in FIG. 6 b, theportable device 100 has a housing 210 to house a communication unit 212for receiving and transmitting information from and to an externaldevice (not shown). The portable device 100 also has a controlling andprocessing unit 214 for handling the received and transmittedinformation, and a virtual display system 230 for viewing. The virtualdisplay system 230 includes a micro-display or an image source 192 andan optical engine 190. The controlling and processing unit 214 isoperatively connected to the optical engine 190 to provide image data tothe image source 192 to display an image thereon. The 3D EPE 20, 20 a or20 b, according to the present invention, can be optically linked to anoptical engine 190.

Furthermore, the image source 192, as depicted in FIG. 6, can be asequential color LCOS (Liquid Crystal On Silicon) device, an OLED(Organic Light Emitting Diode) array, an MEMS (MicroElectro MechanicalSystem) device or any other suitable micro-display device operating intransmission, reflection or emission.

Moreover, the electronic device 100 can be a portable device, such as amobile phone, personal digital assistant (PDA), communicator, portableInternet appliance, hand-held computer, digital video and still camera,wearable computer, computer game device, specialized bring-to-the-eyeproduct for viewing and other portable electronic devices. However, theexit pupil expander, according to the present invention, can also beused in a non-portable device, such as a gaming device, vending machine,band-o-matic, and home appliances, such as an oven, microwave oven andother appliances and other non-portable devices.

It is to be understood that the above-described arrangements are onlyillustrative of the application of the principles of the presentinvention. Numerous modifications and alternative arrangements may bedevised by those skilled in the art without departing from the scope ofthe present invention, and the appended claims are intended to coversuch modifications and arrangements.

1. An apparatus, comprising: a substrate made of an optical materialhaving a first surface and a second surface; and a three-dimensionaldiffractive element comprising a plurality of pixels disposed on thesubstrate, said three-dimensional diffractive element comprises: atleast one area configured to receive an input optical beam, and at leastone further area configured to provide at least one output optical beamwith an exit pupil expanded in one or two dimensions, wherein at leastpart of the input optical beam is diffracted in said at least one areato provide at least one optical beam substantially within the first andsecond surfaces, and at least part of the at least one optical beam isfurther coupled out of the first or the second surface of the substrateby diffraction in said at least one further area to provide said atleast one output optical beam.
 2. The apparatus according to claim 1,wherein said at least one area and at least one further area aredisposed on at least one of: the first surface, the second surface, andopposite surfaces of said substrate.
 3. (canceled)
 4. The apparatus ofclaim 1, wherein each pixel of said plurality of the pixels has a firstwidth in one direction on said first or second surface, a second widthin a perpendicular to said one direction on said first or secondsurface, and a height.
 5. The apparatus of 4, wherein said height ofsaid pixels in said at least one area is larger than in said at leastone further area.
 6. The apparatus of claim 4, wherein a distancebetween said pixels in said one direction and in said perpendicular tosaid one direction one of: not equal in said at least one area; andequal for all said pixels and said first and second widths are equal forall said pixels.
 7. (canceled)
 8. The apparatus of claim 6, wherein saidpixels in said at least one area are configured to provide said at leastone optical beam substantially in said one direction if the inputoptical beam has a predetermined first wavelength, and to provide saidat least one optical beam substantially in said perpendicular to saidone direction if the input optical beam has a predetermined secondwavelength different from said predetermined first wavelength.
 9. Theapparatus of claim 1, wherein said at least one area has pixels slantedat least in one direction, such that said at least one optical beam issubstantially provided in said at least one direction.
 10. The apparatusof claim 1, wherein said at least one area has at least two types ofpixels with an asymmetric shape and slanted in at least two differentdirections, such that one portion of said at least one optical beam issubstantially provided in one of said at least two different directionsand another portion of said at least one optical beam is substantiallyprovided in another of said at least two different directions.
 11. Theapparatus of claim 10, wherein said at least two different directionsare 180 degrees apart.
 12. The apparatus of claim 1, further comprising:an absorbing material deposited on a surface of the substrate oppositeto the surface of said three-dimensional diffractive element andopposite to said at least one area.
 13. The apparatus of claim 1,further comprising: at least one intermediate area such that the atleast part of the optical beam diffracted in the at least one area isfirst coupled to said at least one intermediate area, which isconfigured to substantially couple, using a further diffraction in saidat least one intermediate area, said at least part of said diffractedoptical beam to the at least one further area to provide said outputoptical beam with a two-dimensional exit pupil expansion of said inputoptical beam.
 14. The apparatus of claim 13, wherein saidthree-dimensional diffractive element comprises two of said at least twointermediate areas and two of said further diffractive elements toprovide two substantially identical images with the expanded exit pupilin the two dimensions from an image comprised in said input opticalbeam, wherein a portion of said at least part of the input optical beamis provided to each of said two intermediate areas which is configuredto substantially couple said portion to a corresponding further area ofsaid two further areas for providing said two substantially identicalimages.
 15. The apparatus of claim 13, wherein said at least oneintermediate area has pixels slanted in at least one direction, suchthat said at least one optical beam is substantially provided in said atleast one direction towards said at least one further area.
 16. Amethod, comprising: receiving an input optical beam by at least one areaof a three-dimensional diffractive element comprising a plurality ofpixels disposed on a substrate made of an optical material; diffractingat least part of the input optical beam in said at least one area toprovide at least one optical beam substantially within the first andsecond surfaces; and coupling out at least part of the diffractedoptical beam of the first or the second surface of the substrate bydiffraction in at least one further area of said three-dimensionaldiffractive element to provide at least one output optical beam with anexit pupil expanded in one or two dimensions.
 17. The method of claim16, wherein said at least one area and at least one further area aredisposed at least one of the following: the first surface, the secondsurface and opposite surfaces on said substrate.
 18. The method of claim17, wherein, each pixel of said plurality of the pixels has a firstwidth in one direction on said first or second surface, a second widthin a perpendicular to said one direction on said first or secondsurface, and a height.
 19. The method of 18, wherein said height of saidpixels in said at least one area is larger than in said at least onefurther area.
 20. The method of claim 18, wherein a distance betweensaid pixels in said one direction and in said perpendicular to said onedirection are not equal. 21-30. (canceled)
 31. An electronic device,comprising: a three-dimensional exit pupil expander comprising: asubstrate made of an optical material having a first surface and asecond surface; and a three-dimensional diffractive element comprising aplurality of pixels disposed on the substrate, said three-dimensionaldiffractive element comprises: at least one area configured to receivean input optical beam, and at least one further area configured toprovide at least one output optical beam with an exit pupil expanded inone or two dimensions, wherein at least part of the input optical beamis diffracted in said at least one area to provide at least one opticalbeam substantially within the first and second surfaces, and at leastpart of the at least one optical beam is further coupled out of thefirst or the second surface of the substrate by diffraction in said atleast one further area to provide said at least one output optical beam;at least one component comprising said substrate; and a light sourcedriver, responsive to an illumination selection signal, for providing adrive signal to a light source in said component for providing saidinput optical beam.
 32. An electronic device of claim 31, wherein saidat least one component is at least one of: a liquid crystal display anda keyboard. 33-34. (canceled)